An embodiment of the present invention relates generally to a high voltage switch, and more particularly, to a high voltage switch utilizing low voltage metal-oxide-semiconductor (MOS) transistors with high voltage breakdown isolation junctions.
As complementary metal-oxide-semiconductor (CMOS) technology advances, channel lengths are reduced, thereby enabling high frequency operations. While it is possible to accommodate more functionality into a smaller area, short-channel transistors present a disadvantage in that limits to the source-drain voltage restrict the ability to apply high supply voltages. This issue is particularly manifested proximate interface sections, such as input/output (I/O) pads.
FIG. 1 shows one prior art system for managing high supply voltages. A low voltage short-channel core is provided with short channel transistors having low source-drain breakdown voltages (BVds). A low supply voltage is either provided from the external source, or by using an internal regulator. To pass the signals from/to the core to/from the higher voltage sections, level shifters are used. Accordingly, such circuits become overly complex.
Unlike the system of FIG. 1, a second prior art system, simplified as shown in FIG. 2, does not require a combination of high and low voltage technology. However, the second system is limited only to certain types of I/Os and the input voltage cannot exceed double the supply voltage. Basically the system of FIG. 2 utilizes transistors with proper gate bias. However, the transistors are susceptible to gate oxide breakdown and the source-drain breakdown voltage BVds remains limited. This can be problematic because the source/drain-to-bulk junction must sustain high voltages.
It is desirable to provide a circuit utilizing low voltage transistors for high voltage needs without an expensive and complex design that is unduly limited by the breakdown voltages of the transistors.